1. Field of the Invention
The present invention relates to a cleaning device and an image forming apparatus.
2. Description of the Related Art
As a cleaning device adopted in an image forming apparatus such as a copier, a facsimile, and a printer, there is known a blade cleaning system for pressing a cleaning blade made of an elastic member against a circumferential surface of an image carrier being a body to be cleaned and removing toner on the image carrier by scraping off the toner. The blade cleaning system is widely used because of its simple configuration and stable performance.
In recent years, there are increasing demands for improvement of image quality, and to meet the demands, toner having a smaller particle size and a more spherical shape has been developed. The toner having the smaller particle size enables to obtain a high-resolution image which has a higher degree of accuracy and a higher definition, and the toner having the more spherical shape enables to improve a developing property and a transfer property.
However, when the toner having the smaller particle size and the more spherical shape is used, it is becoming difficult for an ordinary cleaning blade system to perform satisfactory cleaning. This is caused by the reason explained as follows. That is, the cleaning blade removes toner particles while slidably contacting the surface of the image carrier. However, because a portion of an edge of the cleaning blade is deformed, so-called stick slip, caused by a frictional resistance with the image carrier, there occurs a fine space between the image carrier and the cleaning blade. If the toner particles have the smaller particle size, then the toner particles more easily enter this space. If the toner particles having entered the space are closer to sphericity, then rotational moment is generated in the toner particles, and thus the toner particles easily rotate in the space. Therefore, the toner particles having the smaller particle size and the more spherical shape push up the cleaning blade and become easy to enter the space between the cleaning blade and the image carrier.
When the toner particles having the smaller particle size and the more spherical shape are to be used, it can be considered to enhance a pressing force (linear pressure) of the cleaning blade with respect to the image carrier, to prevent the toner particles from entering the space. However, by enhancing the pressing force to apply heavy load to the image carrier, the wearing of the image carrier and the cleaning blade proceeds, which causes their life to be extremely reduced. Recently, because prolonged life of the devices is required, such an inconvenience related to durability has to be avoided.
Like cleaning devices described in Japanese Patent Application Laid-open No. 2002-202702 and Japanese Patent Application Laid-open No. 2007-25173, by adopting an electrostatic cleaning system, even if toner is obtained through a polymerization method, the toner can be satisfactorily cleaned off. Moreover, even if the toner particles to be removed have positive and negative charge polarities, the toner particles can be satisfactorily cleaned off. The cleaning device described in Japanese Patent Application Laid-open No. 2002-202702 includes a conductive blade which is provided on the upstream of a cleaning brush being a cleaning member and is in contact with the image carrier, and to which a voltage having a polarity opposite to that of the cleaning brush is applied, the conductive blade being as a polarity control unit for changing the charge polarities of the toner particles to one of the polarities. According to the cleaning device described in Japanese Patent Application Laid-open No. 2002-202702, when residual toner after transfer passes through a position (blade contact position) where the conductive blade is in contact with the image carrier, the charge polarities of the toner particles are made the same as the charge polarity of the conductive blade (generally, normal charge polarity of toner), caused by charge injection from the conductive blade. In this way, the charge polarities of the toner particles having passed through the blade contact position and having reached a position (roller contact position) where the cleaning brush is in contact with the image carrier are made to be one of the polarities (same polarity as that of the conductive blade). Therefore, even if toner particles having a positive polarity and toner particles having a negative polarity coexist before the cleaning, they can be electrostatically collected by the cleaning brush.
The cleaning device described in Japanese Patent Application Laid-open No. 2007-25173 includes a first cleaning brush to which a voltage (positive polarity) having a polarity opposite to a normal charge polarity of toner is applied, and a second cleaning brush, provided on a downstream of the first cleaning brush, to which a voltage having the same polarity as the normal charge polarity of toner is applied. The toner having the normal charge polarity (negative polarity) on the image carrier is electrostatically attracted to the first cleaning brush being a normally-charged-toner cleaning member and is removed from the image carrier, and the toner having the polarity (positive polarity) opposite to the normal charge polarity on the image carrier is electrostatically attracted to the second cleaning brush being an oppositely-charged-toner cleaning member and is removed from the image carrier. This enables the toner having the positive polarity and the toner having the negative polarity to be removed from the image carrier.
However, in the cleaning devices configured as described in Japanese Patent Application Laid-open No. 2002-202702 and Japanese Patent Application Laid-open No. 2007-25173, when an un-transferred toner image such as a toner pattern in which a large amount of toner adheres to the image carrier is input to the cleaning device, the toner cannot be satisfactorily removed from the image carrier, which results in a cleaning failure.
Therefore, the present applicant(s) has proposed the following cleaning device in Japanese Patent Application No. 2009-293120. More specifically, in the cleaning device described in Japanese Patent Application Laid-open No. 2002-202702, a pre-cleaning brush, which roughly removes toner having a normal charge polarity, is provided on the upstream side of the polarity control unit in the image-carrier-surface moving direction, and in the cleaning device described in Japanese Patent Application Laid-open No. 2007-25173, the pre-cleaning brush is provided on the upstream side of the first cleaning brush in the image-carrier-surface moving direction. By providing the pre-cleaning brush in the above manner, at the time of inputting an un-transferred toner image to the cleaning device, the toner particles having the normal charge polarity, which occupy almost all of the toner particles that form the un-transferred toner image, are roughly removed by the pre-cleaning brush. Thus, the amount of toner to be input to the polarity control unit and the cleaning brush provided on the downstream side of the pre-cleaning brush is reduced. With this feature, the configuration on the downstream side of the pre-cleaning brush in the image-carrier moving direction enables satisfactory cleaning of the toner which cannot be removed by the pre-cleaning brush, in the configuration of the cleaning device described in Japanese Patent Application Laid-open No. 2002-202702 and the configuration of the cleaning device described in Japanese Patent Application Laid-open No. 2007-25173.
It is found that there remains a problem in the cleaning device proposed by the present applicant(s) that the life of the cleaning brush is unnecessarily reduced depending on setting of a biting depth of the cleaning brush, to the image carrier, which is provided on the downstream side of the pre-cleaning brush in the image-carrier moving direction or setting of a relative speed at its contact portion with the image carrier.
If the amount of the biting depth is larger, a contact width between the brush and the image carrier increases, and its cleaning property thereby increases. In addition, if the relative speed of the brush at the contact portion with the image carrier is faster, there is increased the number of contacts of a portion of the image carrier with the cleaning brush while the portion passes through a contact area with the cleaning brush, thus increasing the cleaning property. However, if the biting depth is set to be larger or the relative speed is made faster, the brush wears quickly, which causes the cleaning brush to be degraded early. Because the cleaning brush needs to remove a large amount of toner, the cleaning property has to be increased by setting the biting depth to be larger or making the relative speed faster. However, the amount of toner to be removed by the cleaning brush provided on the downstream side of the pre-cleaning brush in the image-carrier moving direction is less than that by the pre-cleaning brush. Therefore, the cleaning brush does not need the cleaning property as high as that of the pre-cleaning brush. As explained above, although the cleaning brush provided on the downstream side of the pre-cleaning brush in the image-carrier moving direction does not require the high cleaning property, if the biting depth of the cleaning brush provided on the downstream side and the relative speed thereof are set to the same values as these of the pre-cleaning brush, the life of the cleaning brush provided on the downstream side becomes shorter as compared with the case where the biting depth and the relative speed are set according to the cleaning capability required for the cleaning brush provided on the downstream side.
It is also found that there remains a problem in the proposed cleaning device that the life of the cleaning brush is unnecessarily reduced depending on setting of the biting depth of a collecting roller being a collecting member, to the cleaning brush, for collecting toner adhering to the cleaning brush which is provided on the downstream side of the pre-cleaning brush in the image-carrier moving direction, or depending on setting of the relative speed.
If the amount of the biting depth of the collecting roller to the cleaning brush is larger, a contact width between the brush and the collecting roller increases, and toner collecting capability of the collecting roller thereby increases. In addition, if the relative speed of the collecting roller to the brush is faster at the contact portion between the collecting roller and the cleaning brush, there is increased the contact width of the brush with the surface of the collecting roller in a period in which the brush passes through a contact range with the collecting roller, thus increasing the toner collecting capability of the collecting roller. However, if the biting depth is set to be larger or the relative speed is made faster, then, similarly to the above, the brush wears quickly, which causes the cleaning brush to be degraded early. Because a large amount of toner adheres to the pre-cleaning brush, in order to satisfactorily collect the toner, the toner collecting capability of the collecting roller has to be increased by setting the biting depth of the collecting roller to the brush to be larger or by making faster the relative speed of the collecting roller to the brush. However, the amount of toner adhering to the cleaning brush provided on the downstream side of the pre-cleaning brush is less than that of the pre-cleaning brush. Therefore, even if the toner collecting capability of the collecting roller is not so high, the collecting roller can excellently collect the toner adhering to the cleaning brush on the downstream side. Thus, the toner collecting capability of the collecting roller on the downstream side does not need to be made so high as the toner collecting capability of a pre-collecting roller. As explained above, the collecting roller for collecting toner adhering to the cleaning brush provided on the downstream side of the pre-cleaning brush in the image-carrier moving direction does not require the high cleaning property. Despite that, if the biting depth of the collecting roller on the downstream side and the relative speed thereof are set to the same values as these of the pre-collecting roller, the life of the cleaning brush provided on the downstream side becomes shorter as compared with the case where the biting depth and the relative speed are set according to the toner collecting capability of the collecting roller on the downstream side.
According to the present invention, when an un-transferred toner image is input to the cleaning device, the toner having the normal charge polarity, which occupies almost all of the toner forming the un-transferred toner image, is roughly removed by the pre-cleaning brush roller 101. This reduces each amount of toner input to the normally-charged-toner cleaning member and the oppositely-charged-toner cleaning member. The normally-charged-toner cleaning member electrostatically removes the remaining normally charged toner which cannot be removed by the pre-cleaning member, and the oppositely-charged-toner cleaning member electrostatically removes the toner having the polarity opposite to the normal charge polarity. Thus, even if the un-transferred toner image is input to the cleaning device, the toner can be satisfactorily cleaned off.
Moreover, the toner having the normal charge polarity which cannot be perfectly removed by the pre-cleaning member is electrostatically removed by the normally-charged-toner cleaning member, and, therefore, the following effect can be obtained. That is, the toner having the normal charge polarity, on the body to be cleaned, which cannot be perfectly removed by the pre-cleaning member can be satisfactorily removed as compared with the case where the toner having the normal charge polarity which cannot be perfectly removed by the pre-cleaning member is mechanically removed by the oppositely-charged-toner cleaning member like the cleaning device described in Japanese Patent Application Laid-open No. 2007-25173.
According to the present invention, when an un-transferred toner image is input to the cleaning device, the toner having the normal charge polarity, which occupies almost all of the toner forming the un-transferred toner image, is roughly removed by the pre-cleaning member. This causes the amount of toner, on the body to be cleaned, input to the polarity control unit to decrease, and the toner, on the body to be cleaned, having passed through the pre-cleaning member can be satisfactorily controlled to one of the polarities by the charge polarity control unit. Thus, the charge polarities of toner particles input to the cleaning member are made to one of the polarities and the amount of toner is small, and therefore, the toner on the body to be cleaned which cannot be removed by the pre-cleaning member can be satisfactorily removed. As a result, even if the un-transferred toner image is input to the cleaning device, it can be satisfactorily cleaned off.
By having at least one of the following four configurations, it is possible to prolong the life of the cleaning member provided on the downstream side of the pre-cleaning member in the moving direction of the body to be cleaned without lowering the cleaning property.    1. The relative speed of the cleaning member, to the body to be cleaned, provided on the downstream side of the pre-cleaning member in the moving direction of the body to be cleaned is set to be slower than the relative speed of the pre-cleaning member to the body to be cleaned.    2. The biting depth of the cleaning member, to the body to be cleaned, provided on the downstream side of the pre-cleaning member in the moving direction of the body to be cleaned is made less than the biting depth of the pre-cleaning member to the body to be cleaned.    3. The relative speed of the collecting member, to the cleaning member, for collecting the toner on the cleaning member provided on the downstream side of the pre-cleaning member in the moving direction of the body to be cleaned is set to be slower than the relative speed of the pre-collecting member to the pre-cleaning member.    4. The biting depth of the collecting member, to the cleaning member, for collecting the toner on the cleaning member provided on the downstream side of the pre-cleaning member in the moving direction of the body to be cleaned is made less than the biting depth of the pre-collecting member to the pre-cleaning member.
Like the present invention, by having the configuration 1, the wearing of the cleaning member, due to the body to be cleaned, provided on the downstream side of the pre-cleaning member in the moving direction of the body to be cleaned can be suppressed as compared with the case where the relative speed of the cleaning member is set to the same as the relative speed of the pre-cleaning member to the body to be cleaned. Therefore, the life of the cleaning member on the downstream side can be prolonged as compared with the case where the relative speed of the cleaning member, to the body to be cleaned, provided on the downstream side of the pre-cleaning member in the moving direction of the body to be cleaned is set to the same as the relative speed of the pre-cleaning member to the body to be cleaned.
If the relative speed of the cleaning member, to the body to be cleaned, provided on the downstream side of the pre-cleaning member in the moving direction of the body to be cleaned is set to be slower than the relative speed of the pre-cleaning member to the body to be cleaned, the cleaning property decreases. However, as explained above, because the cleaning device according to the present invention is provided with the pre-cleaning member and the toner on the body to be cleaned is removed by the pre-cleaning member, a small amount of toner is input to the cleaning member on the downstream side of the pre-cleaning member in the moving direction of the body to be cleaned. Therefore, even if the cleaning property of the cleaning member is not so high as that of the pre-cleaning member, the cleaning member can satisfactorily clean off the toner on the surface of the body to be cleaned. Because of this, even if the relative speed of the cleaning member, to the body to be cleaned, provided on the downstream side of the pre-cleaning member in the moving direction of the body to be cleaned is set to be slower than the relative speed of the pre-cleaning member to the body to be cleaned and the cleaning property is thereby lowered, a cleaning failure will never occur. Thus, even if the relative speed of the cleaning member, to the body to be cleaned, provided on the downstream side of the pre-cleaning member in the moving direction of the body to be cleaned is set to be slower than the relative speed of the pre-cleaning member to the body to be cleaned, excellent cleaning performance can be maintained.
Like the present invention, by having the configuration 2, the wearing of the cleaning member, due to the body to be cleaned, provided on the downstream side of the pre-cleaning member in the moving direction of the body to be cleaned can be suppressed as compared with the case where the biting depth of the cleaning member to the body to be cleaned is set to the same as the biting depth of the pre-cleaning member to the body to be cleaned. Therefore, the life of the cleaning member on the downstream side can be prolonged as compared with the case where the biting depth of the cleaning member on the downstream side to the body to be cleaned is set to the same as the biting depth of the pre-cleaning member to the body to be cleaned.
If the biting depth of the cleaning member, to the body to be cleaned, provided on the downstream side of the pre-cleaning member in the moving direction of the body to be cleaned is made less than the biting depth of the pre-cleaning member to the body to be cleaned, the cleaning property decreases. However, as explained above, because the cleaning device according to the present invention is provided with the pre-cleaning member and the toner on the body to be cleaned is removed by the pre-cleaning member, a small amount of toner is input to the cleaning member on the downstream side of the pre-cleaning member in the moving direction of the body to be cleaned. Therefore, even if the cleaning property of the cleaning member is not so high as that of the pre-cleaning member, the cleaning member can satisfactorily clean off the toner on the surface of the body to be cleaned. Because of this, even if the biting depth of the cleaning member, to the body to be cleaned, provided on the downstream side of the pre-cleaning member in the moving direction of the body to be cleaned is made less than the biting depth of the pre-cleaning member to the body to be cleaned and the cleaning property is thereby lowered, excellent cleaning performance can be maintained.
Like the present invention, by having the configuration 3, the wearing of the cleaning member, due to the collecting member, provided on the downstream side of the pre-cleaning member in the moving direction of the body to be cleaned can be suppressed as compared with the case where the relative speed of the collecting member to the cleaning member is set to the same as the relative speed of the pre-collecting member to the pre-cleaning member. Thus, the life of the cleaning member on the downstream side can be prolonged as compared with the case where the relative speed of the collecting member, to the cleaning member, for collecting the toner on the cleaning member provided on the downstream side of the pre-cleaning member in the moving direction of the body to be cleaned is set to the same as the relative speed of the pre-collecting member to the pre-cleaning member.
If the relative speed of the collecting member to the cleaning member is reduced, the toner collecting capability of the collecting member decreases. When the relative speed of the collecting member to the cleaning member is reduced and the toner collecting capability of the collecting member is lowered, the toner cannot be collected to the collecting member, which may cause uncollected toner remaining on the cleaning member to increase. If the uncollected toner remaining on the cleaning member increases, the amount of new toner to adhere from the body to be cleaned to the cleaning member decreases, which may cause the cleaning property to decrease. However, as explained above, because the present invention is configured to remove the toner on the body to be cleaned by the pre-cleaning member, a small amount of toner is input to the cleaning member on the downstream side of the pre-cleaning member in the moving direction of the body to be cleaned. Therefore, because a small amount of the toner adheres to the cleaning member on the downstream side, even if the toner collecting capability of the collecting member is decreased, the toner on the cleaning member can be satisfactorily collected. Thus, even if the relative speed of the collecting member, to the cleaning member, for collecting the toner on the cleaning member on the downstream side of the pre-cleaning member in the moving direction of the body to be cleaned is set to be slower than the relative speed of the pre-collecting member to the pre-cleaning member, and even if the collecting capability is thereby decreased, excellent cleaning performance can be maintained.
Like the present invention, by having the configuration 4, the wearing of the cleaning member, due to the collecting member, provided on the downstream side of the pre-cleaning member in the moving direction of the body to be cleaned can be suppressed as compared with the case where the biting depth of the collecting member to the cleaning member is set to the same as the biting depth of the pre-collecting member to the pre-cleaning member. Therefore, the life of the cleaning member on the downstream side can be prolonged as compared with the case where the biting depth of the collecting member, to the cleaning member, for collecting the toner on the cleaning member provided on the downstream side of the pre-cleaning member in the moving direction of the body to be cleaned is set to the same as the biting depth of the pre-collecting member to the pre-cleaning member.
If the biting depth of the collecting member to the cleaning member is reduced, the toner collecting capability of the collecting member decreases. When the toner collecting capability of the collecting member decreases, the cleaning property may decrease similarly to the above. However, as explained above, because the present invention is configured to remove the toner on the body to be cleaned by the pre-cleaning member, a small amount of toner is input to the cleaning member on the downstream side of the pre-cleaning member in the moving direction of the body to be cleaned. Therefore, because there is a small amount of the toner to adhere to the cleaning member on the downstream side, even if the toner collecting capability of the collecting member is decreased, the toner on the cleaning member can be satisfactorily collected. Thus, even if the biting depth of the collecting member, to the cleaning member, for collecting the toner on the cleaning member provided on the downstream side of the pre-cleaning member in the moving direction of the body to be cleaned is made less than the biting depth of the pre-collecting member to the pre-cleaning member and the collecting capability is decreased, excellent cleaning performance can be maintained.